Fluorescent material

ABSTRACT

A fluorescent material is an alkaline earth metal boron phosphate activated by a divalent europium compound having the formula m(Sr1-x-y-pBaxCayEupO)x(1-n)P2O5nB2O3 wherein parameters x, y, p, m and n are respectively in the ranges: 0&lt;/=x&lt;/=0.5 0&lt;/=y&lt;/=0.2 0.001&lt;/=p&lt;/=0.15 1.75&lt;/=m&lt;/=2.30 0.05&lt;/=n&lt;/=0.

BACKGROUND OF THE INVENTION

The present invention relates to novel bluish green emitting fluorescentmaterials of alkaline earth metal boron phosphates activated by adivalent europium compound.

In the specification, the fluorescent material means "phosphor" and theboron phosphate means "borate phosphate".

Heretofore, it has been well-known that strontium-magnesium phosphateactivated with copper (Sr,Mg)₃ (PO₄)₂ :Cu and calcium halophosphateactivated by antimony Ca₁₀ (PO₄)₆ (F,Cl)₂ :Sb are used as typicalfluorescent material emitting in bluish green wavelength region underexciting it by ultraviolet radiation or cathode radiation.

However, these known fluorescent materials have disadvantages to beunsatisfactory from the practical viewpoints.

When the flourescent material of a phosphate activated by copper is usedfor a low pressure or high pressure mercury discharge lamp, it isdifficult to avoid a trouble of a serious decrease of luminous outputbecause the activator of copper is oxidized by heating (such as 600° C.)in a baking step (lehring) for the fluorescent material in thepreparation of a flurorescent lamp.

The fluorescent material of a halophosphate activated by antimony haswide luminous regions so as to emit an emission energy even innear-ultraviolet wavelength region as invisible region. Accordingly, itis difficult to obtain satisfactory luminous efficiency by using it in adischarge lamp for lightening.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above-mentioneddisadvantages and to provide novel bluish green emitting fluorescentmaterials which are not inactivated in a baking step for a preparationof a fluorescent lamp and whose luminous efficiency is high.

The foregoing and other objects of the present invention have beenattained by providing a novel fluorescent material of an alkaline earthmetal boron phosphate activated by a divalent europium compound havingthe formula m(Sr_(1-x-y-p) Ba_(x) Ca_(y) Eu_(p) O)·(1-n)P₂ O₅ ·nB₂ O₃wherein parameters x,y,p,m and n are respectively in the ranges:

0≦x≦0.5

0≦y≦0.2

0.001≦p≦0.15

1.75≦m≦2.30

0.05≦n≦0.23

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fluorescent material of the present invention can be obtained byblending raw materials having suitable element for the formula such asCaCO₃, SrCO₃, CaHPO₄, SrHPO₄, BaHPO₄, H₃ BO₃, Eu₂ O₃ etc., at ratios forforming the formula.

The mixture is charged in a heat resistant vessel such as a silicacrucible, and it is calcined at about 1,000°to 1,200° C. for suitabletime in a reducing atmosphere such as a mixed gas of nitrogen andhydrogen.

The raw materials can be compounds of each element which can beconverted to the corresponding oxide by a thermal decomposition. Thatis, hydroxides, nitrates, oxalates of each element can be used as rawmaterials.

The phosphate source and the boron oxide source should be used.

As described below, the fluorescent materials of the present inventionemits bluish green light under exciting it by ultraviolet rays havingshort or long wavelength, blue visible radiation or cathode radiation.

Te fluorescent material having the formula wherein x=0 and y=0, isstrontium boron phosphate having the formula

    m(Sr.sub.1-p Eu.sub.p O)·(1-n)P.sub.2 O.sub.3 ·nB.sub.2 O.sub.3.

This fluorescent material emits bluish green light under the emissionpeak at 480 nm.

When barium component is added to the strontium component to beparameter x=about 0.5 as maximum content, the wavelength for theemission peak is shifted to longer wavelength side to be about 490 nm.

When calcium component is added to the strontium component, in saidrange of y, the emission spectrum is not substantially changed.

The maximum parameters x and y are defined to be 0.5 and 0.2, becausethe luminous output is remarkably decreased and blue light having theemission peak at about 410 to 430 nm is emitted if these values arehigher.

The blue light has low luminous output to be low practical value.

The parameters of m and n in the formula can be selected as desired insaid ranges. It is most preferable to be in the ranges of 1.9≦m≦2.1 and0.14≦n≦0.18, since the maximum luminous output can be obtained byselecting the parameters of m and n in said ranges.

The europoium content as the parameter p is defined in said range,because an absorption of excited radiation is not enough and effectiveluminous output cannot be obtained when the parameter p is smallerwhereas a quantum efficiency is too low to use in a practical purposewhen the parameter p is higher.

It is most preferable to be in the range of 0.005≦p--0.05 because thefluorescent material having remarkably high luminous ouptut can beobtained.

As described above, the fluorescent material of the present inventioncan be used for a fluorescent layer in a low pressure or high pressuremercury discharge lamp or a cathode-ray tube. It is most preferable touse in a low pressure mercury discharge lamp from the viewpoints ofdegree of luminous output and position of emission spectrum.

In the preparation of the fluorescent layer for the mercury dischargelamp, the fluorescent material is dispersed in an organic solvent (suchas butyl acetate) or water containing a binder for preliminary forming acoated film such as nitrocellulose.

The fluorescent material of the present invention is chemically stablein these solvents without deterioration for a long time. In the bakingprocess for removing the binder by heating (about 600° C.), thefluorescent material is highly stable and the luminous efficiency is notsubstantially decreased.

The luminous efficiency of the strontium-magnesium phosphate activatedby copper as the known fluorescent material is usually decreased toabout 50 to 80% by the baking process at about 600° C. whereas that ofthe fluorescent material of the present invention is only about 2 to 5%.

That is, the fluorescent material of the present invention hassubstantially no trouble in comparison with those of the knownfluorescent materials.

The most important advantages of the fluorescent material of the presentinvention is to be excited by visible blue radiation as well asultraviolet radiation.

The blue color mercury line spectrum at 405 nm and 436 nm emitted from amercury discharge lamp does not substantially contribute for luminousefficiency because such blue light is quite less sensitive as visiblelight.

The fluorescent material of the present invention absorbs such bluelight to convert it to bluish green light which is highly sensitive asvisible light.

When the fluorescent material of the present invention is used for thelow pressure mercury discharge lamp (fluorescent lamp), the luminousefficiency (lm/W) is at least the same or about 50% higher than that ofthe calcium halophosphate activated by antimony, because the fluorescentmaterial of the present invention gives high quantum efficiency and itis excited even by the blue mercury line spectrum to concentrateluminous energy in the range of wavelength of about 440 to 570 nm and toemit substantially no energy in short wavelength region shorter than 440nm.

The fluorescent material of the present invention has said excellentluminous characteristics and various advantageous characteristics andthe industrial advantages are significant.

The present invention will be further illustrated by certain examples.

EXAMPLES 1 to 7 and REFERENCE

The raw materials were blended at ratios shown in Table 1 to obtainmixtures.

Each mixture was charged in a silica crucible and was fired at thetemperature shown in Table 1 in an atmosphere of a mixed gas of nitrogenand hydrogen, for 3 hours.

The volumetric ratio of nitrogen to hydrogen was about 20:1 though itcan be varied to a desired ratio. The trivalent europium was reduced tothe divalent europium.

Each fired product obtained by the firing was quenched and pulverized assieved to obtain each fluorescent material having the formula shown inTable 1.

In the emission spectrum of each fluorescent material, the wavelengthfor the emission peak is shown in unit of nanometer (nm). Thefluorescent materials emit bluish green light having the emission peakat wavelength of about 480 to 490 nm.

A luminous output of each fluorescent material under exciting byultraviolet radiation having wavelength of 254 nm was measured andcompared with a luminous output of the known calcium halophosphateactivated by antimony. A luminous output ratio (energy ratio) of eachfluorescent material to the known calcium halophosphate activated byantimony as 100 is shown in Table 1.

The luminous output ratios of the fluorescent materials of the presentinvention were higher than 100.

                                      TABLE 1                                     __________________________________________________________________________                                         Temp. for                                                                           Wavelength                                                                           Relative                                                 Raw material &                                                                        firing                                                                              for emission                                                                         luminous                    Example                                                                             Chemical Formula       ratios (mole)                                                                         (°C.)                                                                        peak (nm)                                                                            output                      __________________________________________________________________________    1     2Sr.sub.0.98 Eu.sub.0.02 O . 0.84P.sub.2 O.sub.5 0. 16B.sub.2                 O.sub.3                SrHPO.sub.4                                                                        1.68                                                                             1140  480    42                                                       SrCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        2     2Sr.sub.0.84 Ba.sub.0.14 Eu.sub.0.02 O . 0.84 P.sub.2 O.sub.5 .               0.16B.sub.2 O.sub.3    SrHPO.sub.4                                                                        1.68                                                                             1120  480    132                                                      BaCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        3     2Sr.sub.0.84 Ca.sub.0.14 Eu.sub.0.02 O . 0.84 P.sub.2 O.sub.5 .               0.16B.sub.2 O.sub.3    SrHPO.sub.4                                                                        1.68                                                                             1150  480    101                                                      CaCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        4     2Sr.sub.0.68 Ba.sub.0.30 Eu.sub.0.02 O . 0.84P.sub.2 O.sub.5 . 0.16           B.sub.2 O.sub.3        SrHPO.sub.4                                                                        1.36                                                                             1100  480    122                                                      BaHPO.sub.4                                                                        0.32                                                                     BaCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        5     2Sr.sub.0.48 Ba.sub.0.50 Eu.sub.0.02 O . 0.84 P.sub.2 O.sub.5 .               0.16B.sub.2 O.sub.3    SrHPO.sub.4                                                                        0.96                                                                             1070  490    107                                                      BaHPO.sub.4                                                                        0.72                                                                     BaCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        6     2Sr.sub.0.78 Ba.sub.0.10 Ca.sub.0.10 Eu.sub.0.02 O . 0.84 P.sub.2             O.sub.5 . 0.16B.sub.2 O.sub.3                                                                        SrHPO.sub.4                                                                        1.56                                                                             1140  480    128                                                      BaHPO.sub.4                                                                        0.12                                                                     BaCO.sub.3                                                                         0.08                                                                     CaCO.sub.3                                                                         0.20                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        7     2Sr.sub.0.58 Ba.sub.0.20 Ca.sub.0.20 Eu.sub.0.02 O . 0.84 P.sub.2             O.sub.5 . 0.16B.sub.2 O.sub.3                                                                        SrHPO.sub.4                                                                        1.16                                                                             1140  480    107                                                      BaHPO.sub.4                                                                        0.40                                                                     CaHPO.sub.4                                                                        0.12                                                                     CaCO.sub.3                                                                         0.28                                                                     H.sub.3 BO.sub.3                                                                   0.32                                                                     Eu.sub.2 O.sub.3                                                                   0.02                                        Reference                                                                           Calcium halophosphate activated with antimony                                                        --   -- --    480    100                         __________________________________________________________________________

FIG. 1 shows emission spectra of the fluorescent materials of Examples1,3,5 and 7 under exciting by ultraviolet radiation 254 nm.

As it is clear from FIG. 1, the fluorescent materials of the presentinvention emit most of the luminous energy in relatively narrow bluishgreen wavelength region and do not substantially emit the luminousenergy in wavelength region shorter than about 440 nm.

In FIG. 1, the broken line shows the emission spectrum of calciumhalophosphate activated by antimony, and the peaks height of thespectrum is given as 100.

The emission spectra of Examples 2,4 and 6 are not shown in FIG. 1 andthey are respectively similar to those of Examples 1, 5 and 1.

FIG. 2 shows an excitation spectrum of the fluorescent material ofExample 1. In FIG. 2, the relative luminous output ratio is shown asfunction of wavelength of excited radiation under the consideration ofthe maximum luminous ouput as 100.

As it is clear from FIG. 2, the fluorescent material of the invention issatisfactorily excited even by ultraviolet radiation having shortwavelength or long wavelength and also by visible blue radiation.

The excitation spectra of the fluorescent materials of Examples 2 to 7are substantially the same with that of Example 1.

Each straight tube type fluorescent lamp (40W) was prepared by using thefluorescent material of Example 1 and 3 and the known calciumhalophosphate activated by antimony and the characteristics of each lampwere tested. The results are shown in Table 2.

                  Table 2                                                         ______________________________________                                                    Luminous   Luminous                                                           efficiency at                                                                            efficiency at                                                      zero hour of                                                                             500 hours of                                                                             Maintenance                                             lightening lightening factor                                      Fluorescent (lm/W)     (lm/W)     %                                           material    A          B          100 × (B/A)                           ______________________________________                                        Example 1   68.2       66.9       98.1                                        Example 3   47.0       46.2       98.3                                        Calcium halo-                                                                 phosphate activated                                                                       45.0       42.4       94.2                                        with antimony                                                                 ______________________________________                                    

It is clear from Table 2 that the fluorescent lamps using thefluorescent materials of the present invention have excellent superiorcharacteristics on the luminous efficiency and the maintenance factor tothose of the reference.

Various fluorescent materials were prepared by varying parameters m,nand p in the formula of Example 1 and the luminous outputs of thefluorescent materials were measured. The results are shown in FIGS. 3,4and 5.

FIG. 3 shows a relation of the relative luminous outputs to the value mof the fluorescent materials having the formula m(Sr₀.89 Eu₀.02O)·0.84P₂ O₅ ·0.16B₂ O₃ (excited by ultraviolet radiation havingwavelength of 254 nm).

It is clear from FIG. 3, that effective luminous output is obtained inthe range of m=1.75 to 2.30 especially m=1.90 to 2.10.

FIG. 4 shows the relation of the relative luminous outputs to the valuen of the fluorescent materials having the formula

    (SR.sub.0.98 Eu.sub.0.02 O)·(1-n)P.sub.2 O.sub.5 ·nB.sub.2 O.sub.5.

It is clear from FIG. 4, the specific lumination according to thepresent invention can be given in a range of n=0.05 to 0.23, and highluminous output can be given in a range of n=0.14 to 0.18.

FIG. 5 shows a relation of the relative luminous outputs to the value pof the fluorescent materials having the formula

    (Sr.sub.1-p Eu.sub.p O)0.84P.sub.2 O.sub.5 ·0.16B.sub.2 O.sub.3.

It is clear from FIG. 5, effective luminous output is obtained in arange of p=0.001 to 0.15 and especially in a range of p=0.005 to 0.05.

In these figures, strontium was used as the alkaline earth metal. Thus,it was confirmed that the substantially same tendency is given in thecase of barium or calcium when the content is in said range.

As it is clear from these examples and description, the fluorescentmaterials of the present invention are alkaline earth boron phosphatesactivated by divalent europium compound.

According to various analyses such as X-ray diffraction analysis,chemical elementary analysis and luminous characteristic analysis, itwas found that these fluorescent materials are in a form of singlecompound though a crystalline structure is not clearly found.

In the X-ray diffraction analysis, the fluorescent materials of thepresent invention impart the specific X-ray diffraction data.

When the parameter m or n of the fluorescent material is out of saidrange, a different compound is partially formed together with thefluorescent material of the present invention.

That is, in the latter case, the different diffraction fringe which isdifferent from the specific diffraction fringe of the fluorescentmaterial of the present invention is found and the luminous output islowered, as practical disadvantageous problems.

FIG. 6 shows X-ray diffraction spectrum of the fluorescent material ofExample 1.

EXAMPLE 8 (Preparation)

The fluorescent material of Example 1 was prepared as follows.

    ______________________________________                                        SrHPO.sub.4       308.4g (1.68 mole)                                          SrCO.sub.3        41.33g (0.28 mole)                                          H.sub.3 BO.sub.3  19.74g (0.32 mole)                                          Eu.sub.2 O.sub.3  7.04g (0.02 mole)                                           ______________________________________                                    

The raw materials were charged in a ball mill made of alumina, and mixedand pulverized to prepare a mixture. The mixture was charged in a silicacrucible and fired at 1140° C. for 3 hours in an electric furnace in anatmosphere of a mixed gas of nitrogen and hydrogen (volumetric ratio ofN:H=20:1). The fired product was quenched and pulverized and sieved. Theresulting fluorescent material emitted bluish green light under excitingit by ultraviolet radiation or cathode radiation.

According to a chemical analysis, the result was substantially confirmedwith that of the compound 2Sr₀.98 Eu₀.02 O·0.84 P₂ O₅ 0.16 B₂ O₃.

According to X-ray diffracton analysis of the fluorescent material, theX-ray- diffraction spectrum being substantially the same with FIG. 6 wasobtained.

EXAMPLE 9 (Preparation)

    ______________________________________                                        SrHPO.sub.4       308.4g (1.68 mole)                                          Sr(NO.sub.3).sub.2                                                                              59.26g (0.28 mole)                                          H.sub.3 BO.sub.3  19.79g (0.32 mole)                                          Eu.sub.2 O.sub.3  7.04g (0.02 mole)                                           ______________________________________                                    

The raw materials were mixed with 500 cc of water and they werethoroughly stirred and dried on an evaporating dish in a drier heated at150° C. The dried mixture was charged in a silica crucible and fired at1130° C. for 2 hours in a mixed gas of nitrogen and hydrogen (volumetricratio of N:H=20:1) containing 1.5 vol % of steam. The product wasquenched and pulverized and sieved to obtain th fluorescent materialhaving the same formula with that of Example 1. The fluorescent materialcan be used without any treatment.

EXAMPLE 10 (Preparation)

The raw materials of Example 8 were charged and mixed in a ball mill.The mixture was charged in a silica crucible and fired at 1000° C. for 1hour in air. The product was quenched and pulverized and sieved andthen, the product was further fired at 1150° C. for 1.5 hours in a mixedgas of Example 9 containing 1.5 vol % of steam. The product was quenchedand pulverized and sieved to obtain the fluorescent material of thepresent invention.

The fluorescent material emitted bright bluish green light underexciting it by ultraviolet radiation or cathode radiation.

What is claimed is:
 1. An alkaline earth metal boron phosphatefluorescent material activated by divalent europium having the formulam(Sr_(1-x-y-p) Ba_(x) Ca_(y) Eu_(p) O)·(1-n)P₂ O₅ ·nB₂ O₃ whereinparameters x,y,p,m, and n are respectively in the ranges:0≦x≦0.5 0≦y≦0.20.001≦p≦0.15 1.75≦m≦2.30 and 0.05≦n≦0.23.
 2. A fluroescent materialaccording to claim 1 wherein the parameters m and n are in theranges:1.9≦m≦2.1 and 0.14≦n≦0.18.
 3. A fluorescent material according toclaim 1 wherein the parameter p is in the range:0.005≦p≦0.05.